The present invention relates to the packaging of integrated circuits, and in particular to the packaging of monolithic microwave integrated circuits (MMICs) to effect energy transmission at RF frequencies.
Various conventional integration and packaging techniques are known for packaging integrated circuits on substrates. For the most part, these substrates have been either ceramic or metal/ceramic, as shown in U.S. Pat. Nos. 4,780,572 and 3,934,336.
Packaging of MMICs presents a variety of problems. One problem relates to heat dissipation. Another problem relates to the ability of a substrate on which the MMICs are mounted to act as a suitable transmission medium at RF frequencies. Yet another problem relates to difficulties in substrate fabrication, relative to both die bonding of MMICs within recesses in a motherboard, and wire bonding to effect proper electrical connections.
The above-mentioned patents do not disclose the packaging of MMICs on substrates per se, and thus are silent regarding MMIC-specific considerations. However, these patents are exemplary of the types of substrates used to package MMICs.
U.S. Pat. No. 4,199,777, also unrelated to MMIC packaging per se, teaches, in one embodiment, the use of a silicon substrate or motherboard on which semiconductor devices are placed. However, there is no mention of the use of the substrate as a transmission medium for energy at any particular frequency. At most, the substrate might act as a transmission medium for energy at digital or low frequencies, but such certainly is not specifically stated. Further, the placement of semiconductor devices in etched recesses in the substrate is effected by provision of a conformal material which fills in gaps in the recesses. Still further, the silicon substrate disclosed is intended to perform an active function with respect to circuit operation.
None of the prior art of which the inventors are aware uses a silicon motherboard as a passive element, for transmission of energy at RF frequencies. Further, it would be desirable to have a substrate which can be etched so as to facilitate placement and positioning of MMICs, enabling the use of automated die and wire bonding techniques.